Roots of rap music

The first rap record is generally acknowledged to have been "King Tim III" by the Fatback Band in 1979, but there were many predecessors and early indicators of the possibilities of chanting rhymes over a musical background. Pure hip hop emerged from 1970s block parties in New York City. The block parties were closely related to sound systems in Jamaica, which were large parties, originally outdoors, thrown by owners of loud and expensive stereo equipment which they could share with the community. Rap emerged from block parties after DJs isolated percussion breaks and began speaking over the beats; in Jamaica, a similar vocal style called dub developed from the same isolated and elongated percussion breaks.

Earlier styles that contributed to rap

West African griots, wandering poets and "praise-singers"

spirituals and other forms of Christian music, as well as certain Protestant preachers' sermons
mouth music, long-standing tradition in world music of many varieties
scat singing, using the voice to imitate a musical instrument.
toasting, traditional African-American entertainment, long, rhymed tales of great heroes, Stagger Lee and Jack Johnson among others (see dub)
Dirty Dozens, stylized exchange of insults.
"Signifying Monkey", long series of rhymed tales in which the weaker monkey triumphs through tricks over the more powerful beasts of the jungle, a ruder version of the Brer Rabbit stories.
talking blues, popularized by Woodie Guthrie, featuring rhyming talking with ironic asides to the audience.
Late 1960s and early 70s poets like Gil Scott-Heron and the Last Poets
jump rope and schoolyard rhymes, such as the following:

One bright day in the middle of the night,

Two dead boys got up to fight.

Back to back they faced each other,

drew their swords and shot each other.

Doo wop, using voices to imitate an entire band.

Individual performances that prefigured rap

While rap as a musical genre started in the 80s, there have been many black and white performers who succeeded with rap-style performances in early jazz, blues, pop, and country performances.

Pinetop Smith's "Pinetop's Boogie Woogie" (1929) in which the "girl with the red dress on" was first told "when I say stop, don't you move a peg, when I say go I want you to shake your leg".
W.C. Handy's talking celebration of "Long John Dean, the bold bank robber from Bowling Green".
Rosalind Russell, "Swing" (1953), a "patter song" written by Leonard Bernstein for the Broadway musical Wonderful Town that's just full of rappish talk -- "Old man Mose, kicked that bucket, down in the well, well, well, well ... Fish, it's my favorite dish"
Champion Jack Dupree's "Big Leg Emma's" (1956), rhyming tale of a barrelhouse raid over slow blues piano: "I went down to Big Leg Emma's house, to get myself a drink of gin, but before I got in the house good, the law walked in".
Bo Diddley's "Who do you love?", (1956) a maniacal boast, "I got a tombstone hand and graveyard mind, just 22 and I don't mind dyin'".
Many funk songs by Parliament-Funkadelic, such as the spoken-sung call and response poetry of "Promentalshitbackwashpsychosis Enema Squad (The Doo-Doo Chasers)" (Funkadelic, One Nation Under a Groove, 1978)
Napoleon XIV, "They're coming to take me away ha-ha" (1966), just one demented rhymer, a trap set, and a variable speed tape drive. And, on the B-side, the whole thing in reverse.
Bob Dylan "Subterranean Homesick Blues'' 1960s vocal exercise.
Bonzo Dog Band, "Humanoid Boogie" (1969): "Well, the humanoid boogie's gonna get to number one on the cha-cha-charts voted by the people-eeple-eeple of the record-buying publicoid".
Numerous novelty songs of the 50s and 60s featuring rhythmic readings of rhymed verse (often with melodic choruses), such as "Please Mr. Custer", the tale of a reluctant Indian fighter; "All American Boy", the story of Elvis Presley, "Gitarzan" by Ray Stevens, "He's free as the breeze, He's always at ease, He lives in the jungle and hangs by his knees".